Established after a disastrous family holiday as a site for parents to share information and advice, Justine Roberts's Mumsnet has grown into a national brand with real political clout.

The 13-year-old site has given a voice to a section of the population that had previously been neglected on issues such as nursery reform, miscarriage care and job sharing.

Mumsnet, which has more than 4 million monthly unique users and gets 50m page views a month, employs 70 staff, has an annual turnover of about £4m, hosts 200 local sites, and is an umbrella network for 2,000 bloggers.

"It has an amazing presence and feels like it is gaining pace all the time," said our panel. "It is a phenomenal political campaigning voice."

A former journalist and economist, Roberts is married to Ian Katz, the former Guardian deputy editor and new editor of BBC2's Newsnight. Alongside a range of parenting guides and books, Mumsnet has also expanded into live events and launched Gransnet.